The technical development in the field of cutting shank tools in line with the increasingly higher cutting speeds and the use of program-controlled machine tools leads to tool systems built in modular fashion. For example, on a clamping cylinder of a tool holding fixture that is produced with great precision and thus is very expensive, a system of different tools is attached that must be interchangeable by means of a tool changer that operates automatically.
This development requires a specifically compatible coupling system which successfully guarantees, with sufficient quality, the power transmission from the tool holding fixture or the clamping cylinder to the tool, accuracy of concentricity, and the matching of the position of the tool cutting edges to the shank or to the holding fixture for the entire spectrum of tools that are to be coupled.
In this connection, a series of such coupling systems has already been suggested which, however, only partially fulfill the requirements mentioned above.
It has been suggested, for example, that the coupling be produced through a self-centering Hirth-type serration that, together with a spring chuck, assures an interlocking coupling of the parts to be attached to one another. This suggested solution is expensive as regards production and is limited, depending on the chucking system used, to the coupling point with the base holding fixture. In further coupling points must be provided in the shank region of the tool (for example, for the case where extension pieces or adaptors must be used), different couplings are needed. An automatic tool change is made more difficult in this way.
A further suggestion consists of the coupling of adjacent parts of the shank of the tool occurring through a centric screw coupling. It has been shown that this coupling techniques makes the use of automatic tool changer systems more difficult since, to disengage the coupling, a frontal access to the shank parts is necessary to be able to disengage the connection quickly. Further, it has grown disadvantageous that the coupling of tools with reduced shank diameter is possible only by a simultaneously relatively great increase in the separation of the tool cutting edge from the base holding fixture, which can have a negative effect on the precision of the machining operation.
Finally, to simplify the automated disengagement of the coupling between various shank parts, a solution has been suggested in which a cylindrical centering extension of a shank part is inserted into a holding fixture hole of the adjacent shank part. The outer surface of the centering cylinder contains two diametrically offset recesses that are undercut in the opposite direction so that, when corresponding positioning screws are screwed in, an immovable bracing of the shank part used relative to the holding fixture part can occur. Driving occurs through a mandrel that engages in an axial slot in the centering cylinder. If this is true, the coupling system can be used at any point on the shank tool. However, it assumes an axial position fixing of the shank sections to be coupled with one another during the tightening operation of the fastening screws, by which the use of automatic tool changer systems is made more difficult, since two clamping bolts must be actuated.
Further, a coupling system for a tool system built in a modular fashion has been suggested in which, with a single set screw that can be actuated laterally from outside, the parts that are to be coupled can be fixed in an immobile position relative to one another. For this, in the centering extension a fastening bolt is provided that is mounted to be slidably movable in a diametrically aligned guide hole. A front surface of the fastening bolt contains a conical recess, whereas the outer end surface of the fastening bolt has a conical outer surface. Through an adjusting device formed as a countersunk head bolt, the body of which is matched to the inner recess of the fastening bolt, there occurs a shifting of the fastening bolt in the diametrical bore hold so that the tapered outer surface can brace against a conical recess of a carrying bolt that can be screwed from the other side of the first fastening part. The axis of the fastening bolt is offset relatively to the axis of the countersunk head bolt and the carrying bolt so that, when the countersunk head bolt is screwed in, an axial force can be transmitted to the centering extension so that the parts to be coupled can be put under tension against each other through a prop ring surface pairing. To achieve the positioning and a coupling of both parts in the peripheral direction, an index pin is provided in the region of the prop ring surfaces.
Aside from the fact that, with this solution, a symmetrical distribution of contact pressure can be achieved only when there is a precisely controlled vane position of the support surfaces on the side of the supporting nut and the conical recess in the fastening bolt and, further, a precise alignment of the axial planes of the shank tool that run through the respective axes of the fastening bolt and the carrying bolt, as well as the countersunk head bolt, drawbacks can occur in the sense that, with the use of certain tools, rotating tool vibrations occur which can be countered only in a limited way by the present orientation and position of the support surfaces. Further, with this solution, when the centering extension is formed on the part nearer to the tool cutting edge, the tool system becomes basically more expensive. To counteract this problem, it was suggested that the coupling system be supplemented with an annexed spindle flange on which the centering extension for the holding fixture of the fastening bolt could be attached. However, this variant can lead, especially in shank tools with high thermal stress, to the fact that, when changing the tool (i.e., when putting on a new tool that does not yet have the higher operating temperature of the centering extension), fitting problems occur, due to which down time must be accepted.